Automatic transmission with overdrive device

ABSTRACT

An automatic transmission having a torque converter comprising an impeller connected to the crankshaft of an internal combustion engine and a turbine driven by the impeller by oil, an automatic transmission apparatus comprising a planetary gear device and a fluid operated brake and clutch devices connected to an output shaft of the turbine, an oil pump driven by the impeller through an oil pump drive shaft for producing pressure oil applied to the fluid operated brake and clutch devices, and a final reduction gear device connected to an output shaft of the automatic transmission apparatus. An overdrive device comprising an overdrive clutch and overdrive gears is connected between the oil pump drive shaft and an intermediate shaft. The intermediate shaft is connected between an output shaft of the overdrive gears and the final reduction gear device, and a valve is provided for applying the pressure oil to the overdrive clutch.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic transmission provided withan overdrive device of the type in which a torque converter, anautomatic transmission and a final reduction gear are integrallyassembled, and more particularly relates to an automatic transmissionwhich is directly connected with an engine in the overdrive condition.

In a conventional automatic transmission with an overdrive device, powerfrom the engine crankshaft is transmitted to an overdrive device througha torque converter even in the overdrive condition. In such constructionit has been impossible to attain as low a fuel consumption as with amanual transmission, because of transmission loss due to the torqueconverter in the overdrive condition. Further, planetary gears aregenerally used for a gear mechanism of the overdrive device, since thepower transmission flow is arranged on the axis. Such a constructionmakes the apparatus large and complicated. Also the apparatus should beprovided with at least two pairs of transmission elements, which causecomplication of the hydraulic control system.

SUMMARY OF THE INVENTION

Considering such drawbacks, it is an object of the present inventionprovide an automatic transmission with an overdrive device in which anoil pump driving shaft connected to an impeller of a torque converter isconnected with an oil pump arranged at the rear part of an automatictransmission apparatus and also connected to an overdrive clutch of anoverdrive device without interposing the torque converter, so that thetransmission loss in the torque converter may be eliminated, therebyimproving fuel consumption.

According to the present invention, there is provided an automatictransmission comprising a torque converter comprising an impellerconnected to the crankshaft of an internal combustion engine and aturbine driven by the impeller by oil, an automatic transmissionapparatus comprising a planetary gear device and a fluid operated brakeand clutch devices connected to the output shaft of the turbine, an oilpump driven by the impeller through an oil pump drive shaft forproducing pressure oil applied to the fluid operated brake and clutchdevices, a final reduction gear device connected to an output shaft ofthe automatic transmission apparatus, an overdrive device comprising anoverdrive clutch and overdrive gears, said overdrive clutch beingconnected between the impeller and the overdrive gears, an intermediateshaft connected between an output shaft of the overdrive gears and thefinal reduction gear device, and valve means for applying the pressureoil to the overdrive clutch for engagement thereof.

The present invention will be more fully explained with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The only FIGURE is a skelton drawing showing a preferred embodiment ofthe automatic transmission in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the figure, a trans-axle type transmission 1 is shown for drivingfront wheels, which comprises a torque converter 2, an automatictransmission device 3 for three speeds, a final reduction device 4disposed between the automatic transmission device 3 and the torqueconverter 2, a valve block 5 of a hydraulic control device provided in alower part of the automatic transmission device 3, and an overdrivedevice 6 arranged in a rear part of the automatic transmission device 3opposite the torque converter 2.

The torque converter 2 is in a converter housing 7, and comprises a pumpimpeller 2a, a turbine 2b and a stator 2c. The pump impeller 2a is indirect connection with an engine crankshaft 8 by means of a drive plate9. A turbine shaft 10 is extended from the turbine 2b and an oil pumpdrive shaft 12 extends from a converter cover 11 provided integrallywith the drive plate 9 through a damper 11a. The pump impeller 2a isrotated by the engine by means of the crankshaft 8 to rotate the turbine2b by the oil flow regulated by the stator 2c.

It should be noted that the damper 11a is provided to prevent theinfluence of torque variation occurring during the overdrive conditionfrom acting directly on the converter cover.

The automatic transmission device 3 has a transmission case 13 in whicha planetary gear 14 at its front part, and a low-and-reverse brake 15 atits rear part, a forward clutch 16, and a reverse clutch 17 are arrangedin this order. The turbine shaft 10 which is connected to the turbine 2bof the torque converter 2 is connected to a forward sun gear 14a of theplanetary gear 14 through the forward clutch 16, and at the same time isconnected to a reverse sun gear 14b through the reverse clutch 17 toapply the output of the turbine shaft 10 thereto. Further, a brake band18 is provided on the drum side of the reverse clutch 17 to lock thereverse sun gear 14b. In the planetary gear 14, a short pinion 14cengaging with the forward sun gear 14a and a long pinion 14d engagingwith the reverse sun gear 14b are supported in a carrier 14e whichsupports the low-and-reverse brake 15. The carrier is locked by aone-way clutch 20 provided between the low-and-reverse brake 15 and acenter support 19. An output shaft 21 extends from a ring gear 14f, thelatter engaging with the long pinion 14d, to the torque converter.

The front-wheel final reduction device 4 has a case 22 secured betweenthe converter housing 7 and the transmission case 13. The case 22contains a crown gear 23a of a differential mechanism 23 for frontwheels of the vehicle and is disposed under units including the turbineshaft 10. The output shaft 21 is coupled with a drive pinion 23b bymeans of a reduction gear 24 for transmitting the power to the crowngear 23a.

Further, the valve block 5 of the hydraulic control device containstherein various valves and oil passages (not shown). The hydrauliccontrol device is adapted to supply or discharge the pressure oil to orfrom a servo mechanism of the low-and-reverse brake 15 and the clutches16, 17, and the brake band 18 of the automatic transmission device 3 inaccordance with the transmission pattern according to the relationbetween vehicle speed and engine load.

The overdrive device 6 of the present invention is provided within atransmission cover 25 which is fixed to the rear end of the transmissioncase 13. Disposed between the transmission case 13 and the transmissioncover 25 is an oil pump 27 connected to an oil pump drive shaft 12 whichis engaged with and driven by the engine crankshaft 8. The oil pumpdrive shaft 12 extends into the transmission cover 25 and is connectedto an extension 12'. An overdrive gear device 28 and an overdrive clutch29 are disposed on the extension 12'. The overdrive gear device 28comprises a large drive gear 28a and a small driven gear 28b whichengage each other. The drive gear 28a is freely rotatably mounted on theextension 12' and the driven gear 28b, is secured to a rearwardextension of the drive pinion 23b, so that a speed-up gear device isprovided. An overdrive clutch 29, which is a hydraulic clutch type,comprises a drum 29a secured to the extension 12' and a hub 29b securedto the drive gear 28a, and is adapted to establish or cut off theconnection of the oil pump drive shaft 12 with the drive gear 28a.Further, the driven gear 28b is connected to the drive pinion 23b of thefinal reduction device 4 by means of an intermediate shaft 30 and aspline joint 31.

A clutch support 26 is provided with a valve 32 for changing theoverdrive. The valve 32 is adapted to discharge the oil from the forwardclutch 16 and to supply the oil to the overdrive clutch 29 to achievethe engagement when the vehicle reaches a condition suitable foroverdriving.

Because of such construction of the present invention, when oil isdischarged from the overdrive clutch 29, the overdrive gear device 28 isdisengaged from the oil pump drive shaft 12, so that the drive shaft 12drives only the oil pump 27. If the forward clutch 16 of the automatictransmission device 3 is engaged, power from the engine crankshaft 8 istransmitted to the turbine shaft 10 through the torque converter 2 andfurther to the forward sun gear 14a of the planetary gear 14 toestablish a forward driving speed condition. When the carrier 14e islocked by the one-way clutch 20 or the low-and-reverse brake 15, thelargest gear ratio transmission is provided. From the output shaft 21,the output is transmitted to the drive pinion 23b of the differentialmechanism 23 through the reduction gear 24 and further to the frontwheels through the crown gear 23a to establish the 1st-speed drivingcondition. When the vehicle speed reaches a predetermined speed, thebrake band 18 instead of the low-and-reverse brake 15 actuates to lockthe reverse sun gear 14b. Thus, power transmission of a gear ratiosmaller than the above-mentioned 1st-speed, that is, the 2nd-speeddriving condition is established. When the vehicle speed is furtherincreased, the reverse clutch 17 instead of the brake band 18 isengaged. Accordingly, the planetary gear device is integrated and theturbine shaft 10 and the output shaft 21 are directly connected witheach other to transfer the output from the turbine shaft 10 to the frontwheels, as the 3rd-speed transmission.

If, as an example, during high speed driving in the 3rd-speed condition,when the overdrive clutch 29 is engaged after disengaging the forwardclutch 16 of the automatic transmission device 3 by the valve 32, theplanetary gear 14 becomes incapable of automatic transmission operationbecause no power is applied to the forward sun gear 14a. On thecontrary, the oil pump drive shaft 12 is engaged with the overdrive geardevice 28 as a result of the engagement of the overdrive clutch 29.Thus, power from the oil pump drive shaft 12 which is directly connectedto the engine crankshaft 8 is transmitted to the overdrive gear device28 and the speed is increased by the drive and the driven gears 28a and28b. The power from the intermediate shaft 30 of the driven gear 28b istransmitted to the front wheels through the drive pinion 23b and thecrown gear 23a of the differential mechanism 23. Thus, the vehicle isover-driven by the direct connection condition without transmission lossby fluid in the torque converter.

In this condition, the power transmitted to the turbine shaft 10 throughthe torque converters is applied to the reverse sun gear 14b of theplanetary gear 14 because of the engagement of the reverse clutch 17during the 3rd-speed. The power transmitted to the drive pinion 23b ofthe differential mechanism 23 is reversely applied to the ring gear 14fof the planetary gear 14 through the reduction gear 24 and the outputshaft 21. However, the carrier 14e is free to rotate, since the one-wayclutch 20 and the low-and-reverse brake 15 are released. As a result,the planetary gear 14 idles without causing any effect.

Changing to the overdrive gear device 28 from the 1st-speed drive or the2nd-speed drive may also be performed in the same way as abovedescribed. Operation in the reverse manner causes the overdrivecondition to release and to effect the power transmission by means ofthe automatic transmission device 3.

In accordance with the construction of the present invention, theoverdrive device 6 by direct connection with the engine without passingthrough the torque converter 2 can be provided in the automatictransmission. Therefore, the transmission loss in the torque converter 2is avoided, causing improvement in fuel consumption as well as in outputpower. Since the overdrive device 6 is fixed on the rear part of theautomatic transmission device 3 so as to transmit the power from the oilpump drive shaft 12 to the final reduction device 4, the automatictransmission device 3, the final reduction device 4, and the oil pumpdrive shaft 12 can also be used for the overdrive device 6, whichsimplifies the construction.

What is claimed is:
 1. An automatic transmission comprisinga torqueconverter comprising a converter cover and an impeller connected to acrankshaft of an internal combustion engine and a turbine driven by saidimpeller through oil, an automatic transmission apparatus comprising aplanetary gear device and fluid operated brake and clutch devicesoperatively connected to an output shaft of said turbine, an oil pumpdrive shaft operatively connected to said converter cover and axiallyextending through said automatic transmission apparatus, meanscomprising an oil pump driven by said oil pump drive shaft for producingpressure oil to be applied to the fluid operated brake and clutchdevices, a final reduction gear device connected to an output shaft ofsaid automatic transmission apparatus, an overdrive device comprising anoverdrive clutch and overdrive gears, said overdrive clutch beingconnected between said oil pump drive shaft and said overdrive gears, anintermediate shaft connected between an output shaft of said overdrivegears and said final reduction gear device, and valve means for applyingthe pressure oil to said overdrive clutch for engagement thereof foroverdriving and substantially simultaneously via one of said clutchdevices for operatively disconnecting said output shaft of said turbinefrom said final reduction gear device via said automatic transmissionapparatus and said planetary gear device.
 2. The automatic transmissionaccording to claim 1 whereinsaid overdrive device and said oil pump aremounted at a rear portion of said automatic transmission apparatus, saidoverdrive clutch is connected to a rear portion of said oil pump driveshaft.
 3. An automatic transmission according to claim 1 wherein saidoverdrive clutch is connected to an extension of said oil pump driveshaft.
 4. The automatic transmission according to claim 1, whereinsaidone of said clutch devices is a forward clutch.
 5. The automatictransmission according to claim 1, further comprisinga spline jointwhich connects said intermediate shaft to said final reduction geardevice.
 6. The automatic transmission according to claim 1, furthercomprisingdamper means for connecting said oil pump drive shaft to saidconverter cover.
 7. The automatic transmission according to claim 1,whereinsaid overdrive gears comprise two peripherally engaging gearshaving parallel axes of rotation, one of said overdrive gears is coaxialto and mounted relatively rotatable to said oil pump drive shaft, theother of said overdrive gears is coaxial to said intermediate shaft andis connected to said output shaft of said overdrive gears.
 8. Theautomatic transmission according to claim 2, whereinsaid automatictransmission apparatus is located between said overdrive device and saidtorque converter.
 9. The automatic transmission according to claim 8,whereinsaid oil pump is located between said automatic transmissionapparatus and said overdrive device.
 10. The automatic transmissionaccording to claim 1, whereinsaid torque converter, said automatictransmission apparatus and said overdrive device are axially aligned inthe recited order.
 11. The automatic transmission according to claim 1,whereinsaid output shaft of said turbine is hollow, said oil pump driveshaft is coaxially arranged inside of said output shaft of said turbine.12. An automatic transmission comprisinga torque converter comprising aconverter cover and an impeller connected to a crankshaft of an internalcombustion engine and a turbine driven by said impeller by means of oil,an automatic transmission apparatus comprising a planetary gear set andfluid operated brake and clutch devices operatively connected to anoutput shaft of said turbine, an oil pump drive shaft operativelyconnected to said converter cover and axially extending through saidautomatic transmission apparatus, means comprising an oil pump driven bysaid oil pump drive shaft for producing pressure oil to be applied tothe fluid operated brake and clutch devices, a final reduction geardevice connected to an output shaft of said automatic transmissionapparatus, an intermediate shaft connected to said final reduction geardevice, an overdrive means comprising an overdrive clutch means andoverdrive gears, the latter being separate and independent from saidplanetary gear set of said automatic transmission apparatus, saidoverdrive clutch means upon actuation thereof for receiving the pressureoil from said oil pump and for releasably operatively connecting saidtorque converter to said intermediate shaft via said overdrive gears,valve means for applying the pressure oil to said overdrive clutch meansfor actuation thereof for overdriving and substantially simultaneouslyvia one of said clutch devices for operatively disconnecting said outputshaft of said turbine from said final reduction gear device via saidautomatic transmission apparatus and said planetary gear set, and saidvalve means for releasing said overdrive clutch means and substantiallysimultaneously locking said one clutch device for normal operation ofsaid automatic transmission apparatus.
 13. The automatic transmissionaccording to claim 12, whereinsaid overdrive means and said oil pump aremounted at a rear portion of said automatic transmission apparatus. 14.The automatic transmission according to claim 12, whereinsaid torqueconverter, said automatic transmission apparatus and said overdrivemeans are axially aligned in the recited order.